From the Schulich Heart Program, Sunnybrook Health Sciences Centre (M.G.M.), Institute for Clinical Evaluative Sciences (J.M.P., K.T.), University Health Network–Toronto Western Hospital Family Health Team (K.T.), Department of Medicine (M.G.M.), Department of Family and Community Medicine (K.T.), and Institute of Health Policy, Management and Evaluation (J.M.P., K.T.), University of Toronto, Toronto, Canada; the Department of Family and Emergency Medicine, Université de Montréal, and CRCHUM, Montreal, Canada (J.K.); and the Department of Family Medicine, McMaster University, Hamilton, Canada (J.M.P., J.K., L.D.).

From the Schulich Heart Program, Sunnybrook Health Sciences Centre (M.G.M.), Institute for Clinical Evaluative Sciences (J.M.P., K.T.), University Health Network–Toronto Western Hospital Family Health Team (K.T.), Department of Medicine (M.G.M.), Department of Family and Community Medicine (K.T.), and Institute of Health Policy, Management and Evaluation (J.M.P., K.T.), University of Toronto, Toronto, Canada; the Department of Family and Emergency Medicine, Université de Montréal, and CRCHUM, Montreal, Canada (J.K.); and the Department of Family Medicine, McMaster University, Hamilton, Canada (J.M.P., J.K., L.D.).

From the Schulich Heart Program, Sunnybrook Health Sciences Centre (M.G.M.), Institute for Clinical Evaluative Sciences (J.M.P., K.T.), University Health Network–Toronto Western Hospital Family Health Team (K.T.), Department of Medicine (M.G.M.), Department of Family and Community Medicine (K.T.), and Institute of Health Policy, Management and Evaluation (J.M.P., K.T.), University of Toronto, Toronto, Canada; the Department of Family and Emergency Medicine, Université de Montréal, and CRCHUM, Montreal, Canada (J.K.); and the Department of Family Medicine, McMaster University, Hamilton, Canada (J.M.P., J.K., L.D.).

From the Schulich Heart Program, Sunnybrook Health Sciences Centre (M.G.M.), Institute for Clinical Evaluative Sciences (J.M.P., K.T.), University Health Network–Toronto Western Hospital Family Health Team (K.T.), Department of Medicine (M.G.M.), Department of Family and Community Medicine (K.T.), and Institute of Health Policy, Management and Evaluation (J.M.P., K.T.), University of Toronto, Toronto, Canada; the Department of Family and Emergency Medicine, Université de Montréal, and CRCHUM, Montreal, Canada (J.K.); and the Department of Family Medicine, McMaster University, Hamilton, Canada (J.M.P., J.K., L.D.).

From the Schulich Heart Program, Sunnybrook Health Sciences Centre (M.G.M.), Institute for Clinical Evaluative Sciences (J.M.P., K.T.), University Health Network–Toronto Western Hospital Family Health Team (K.T.), Department of Medicine (M.G.M.), Department of Family and Community Medicine (K.T.), and Institute of Health Policy, Management and Evaluation (J.M.P., K.T.), University of Toronto, Toronto, Canada; the Department of Family and Emergency Medicine, Université de Montréal, and CRCHUM, Montreal, Canada (J.K.); and the Department of Family Medicine, McMaster University, Hamilton, Canada (J.M.P., J.K., L.D.).

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Abstract

The risk of cardiovascular events in relation to blood pressure is largely based on readings taken with a mercury sphygmomanometer in populations which differ from those of today in terms of hypertension severity and drug therapy. Given replacement of the mercury sphygmomanometer with electronic devices, we sought to determine the blood pressure threshold for a significant increase in cardiovascular risk using a fully automated device, which takes multiple readings with the subject resting quietly alone. Participants were 3627 community-dwelling residents aged >65 years untreated for hypertension. Automated office blood pressure readings were obtained in a community pharmacy with subjects seated and undisturbed. This method for recording blood pressure produces similar readings in different settings, including a pharmacy and family doctor’s office providing the above procedures are followed. Subjects were followed for a mean (SD) of 4.9 (1.0) years for fatal and nonfatal cardiovascular events. Adjusted hazard ratios (95% confidence intervals) were computed for 10 mm Hg increments in blood pressure (mm Hg) using Cox proportional hazards regression and the blood pressure category with the lowest event rate as the reference category. A total of 271 subjects experienced a cardiovascular event. There was a significant (P=0.02) increase in the hazard ratio of 1.66 (1.09, 2.54) at a systolic blood pressure of 135 to 144 and 1.72 (1.21, 2.45; P=0.003) at a diastolic blood pressure of 80 to 89. A significant (P=0.03) increase in hazard ratio of 1.73 (1.04, 2.86) occurred with a pulse pressure of 80 to 89. These findings are consistent with a threshold of 135/85 for diagnosing hypertension in older subjects using automated office blood pressure.

Introduction

The management of hypertension has traditionally been based on the measurement of blood pressure (BP) in the office using manual devices, such as the mercury sphygmomanometer. Manual BP measurement is associated with numerous sources of error, the most important of which relate to human behavior. In the office setting, many patients become anxious, health professionals frequently do not follow proper BP measurement technique, and the presence of a nurse or physician leads to conversation, which increases BP. Also, the phasing out of the mercury sphygmomanometer because of concerns about its potential adverse effects on the environment and human health provides further motivation to re-examine the role of manual BP in clinical practice.

In recent years, the pre-eminence of office BP has been challenged by the widespread use of 24-hour ambulatory BP monitoring (ABPM) and self-measurement of BP in the home. The well documented advantages of ABPM1 and home BP2 in evaluating the benefits of antihypertensive therapy for individual patients has led to major changes in recent guidelines for the diagnosis of hypertension. ABPM and home BP have been advocated as the methods of choice for determining the BP status of patients,3–5 whereas manual office BP is being replaced by electronic oscillometric sphygmomanometers, most of which are activated by the office staff. Although these semiautomated devices eliminate some of the errors associated with manual BP measurement, the presence of an observer may still provoke inaccurate BP readings.6,7

This limitation of semiautomated devices has been overcome by the development of accurate oscillometric sphygmomanometers specifically designed for professional use, which take multiple BP readings automatically with the patient resting quietly and alone,8 now referred to as automated office BP (AOBP). Numerous studies comparing AOBP to awake ambulatory BP and home BP have shown that AOBP produces more accurate readings compared with manual BP and virtually eliminates the white coat response.9 Based on these comparative AOBP data, a cut-point of 135/85 mm Hg has been proposed when using AOBP to diagnose hypertension.8

Unlike conventional office BP, AOBP readings do not seem to be affected by the setting in which the BP is recorded, providing the above procedures for AOBP are followed. Readings recorded in an ABPM unit or in an office waiting room are similar to AOBP recorded in a physician’s examining room.10–12 As a corollary to the present study, 275 residents aged over 65 years in 2 midsized communities in Ontario, Canada, had their BP recorded using standard AOBP procedures in a local pharmacy.13 Mean AOBP values were similar to AOBP measurements taken on a visit to the subject’s own family physician, indicating that AOBP-type measurements can also be taken in a pharmacy.

At present, there is only limited evidence relating AOBP readings to intermediate measures of target organ damage, left ventricular mass, and intima-media wall thickness.14,15 The Cardiovascular Health Awareness Program (CHAP) was a BP screening program in which community-dwelling residents in Ontario over age 65 years had their BP recorded in a local pharmacy using the same standard AOBP procedures used as in the above-mentioned pharmacy study.16 Participants in CHAP were followed for the development of nonfatal and fatal cardiovascular events, thus providing an opportunity to relate AOBP readings to future cardiovascular end points.

Methods

CHAP16 was a cluster randomized, controlled trial which examined the effectiveness of a community-based intervention, which included hypertension screening with AOBP in reducing hospitalization as a result of cardiovascular events. In cooperation with local family physicians, pharmacies, and various volunteer organizations, residents aged 65 years and older were invited to attend CHAP sessions to have their BP measured and cardiovascular risk factors documented. Information was also provided on local resources and activities, which focused on cardiovascular health promotion and management. Details of the CHAP intervention and trial results have been previously published.16,17 The protocol for this supplementary analysis of CHAP trial data was approved by the Research Ethics Board of Sunnybrook Health Sciences Center, Toronto.

Study Subjects

All community-dwelling residents aged ≥66 who attended at least one CHAP session were eligible for inclusion in the current study. Exclusions included individuals for whom missing personal identifiers prevented linkage of their BP values with Ontario government health administrative data, persons for whom we had less than a 365-day history of prescription drug claims (which excluded subjects <66 years old), those enrolled in the Ontario Health Insurance Program for <3 years, and those without AOBP readings. Subjects who were already taking antihypertensive medication were excluded from the present analysis.

Procedures

The CHAP intervention included BP recordings taken using a BpTRU device (BpTRU Medical Devices Ltd, Coquitlam, BC, Canada) under the supervision of volunteer lay persons trained by nurses and pharmacists according to the standards of the organization responsible for developing and disseminating guidelines for the diagnosis and management of hypertension in Canada, the Canadian Hypertention Education Program. The Canadian Hypertention Education Program–recommended procedures for AOBP included a requirement for participants to be seated in a quiet place without conversation when the readings were taken.17 In accordance with the Canadian Hypertention Education Program protocol,18 participants were not required to rest for 5 minutes before the first BP measurement.

The fully automated BpTRU device was set to take an initial test reading and then 5 readings at 1 minute intervals with the subject sitting quietly alone without conversation. After the last BP, the device automatically computed the mean of the 5 readings. The participants’ family physicians were informed of the session’s findings by fax, including their patients’ BP reading. Any management decisions, including possible initiation of antihypertensive drug therapy, were left to the discretion of the family physicians.

Data Collection and Outcome Measures

Participants’ baseline characteristics were obtained using a combination of self-administered questionnaire completed during their initial CHAP session (overall health status, height, weight, smoking status, alcohol consumption, and hypercholesterolemia) and Ontario administrative health-care databases. Subjects on drug therapy for hypertension were identified using prescription drug claims stored in the Ontario Drug Benefit Program Database, which captures records of prescriptions dispensed to all Ontarians aged ≥65 years. We used validated administrative data case definitions to identify whether participants had a history of 4 key comorbidities: hypertension,19 congestive heart failure,20 diabetes,21 and end-stage renal disease.22,23

Participants were followed from the date of their first CHAP BP measurement (September to November 2006) to the first of a nonfatal cardiovascular event, death, out-migration, or the end of the study follow-up period (March 31, 2013, for nonfatal cardiovascular events and December 31, 2011, for cardiovascular death because of a 2-year lag period in availability of cause-specific mortality data). Our primary outcome measure was a composite of acute care hospital admissions with a most responsible (primary) discharge diagnosis of acute myocardial infarction, congestive heart failure, or stroke or death with a primary cause of cardiovascular disease. Hospitalizations were captured in the Canadian Institute for Health Information’s Discharge Abstract Database with validated ICD-10-CA (International Classification of Diseases, 10th revision, Canadian enhancement) diagnosis codes with high positive predictive value.24–26 Cardiovascular deaths were captured in the Ontario Registrar General’s Vital Statistics Database using ICD-10 diagnosis codes I00-I78.

Statistical Analysis

Participants’ characteristics were summarized using basic descriptive statistics. Outcome event rates (per person-year of follow-up) were computed (with 95% confidence limits) and tabulated according to systolic and diastolic AOBP category and according to pulse pressure (systolic minus diastolic AOBP). Adjusted hazard ratios (HR) and 95% confidence intervals were computed for 10 mm Hg increments in BP using Cox proportional hazards regression with the BP category having the lowest event rate as the reference category. All analyses were performed at the Institute for Clinical Evaluative Sciences (www.ices.on.ca) on anonymized, encoded records using SAS version 9.3 (SAS Institute, Cary, NC) and a 2-tailed type 1 error rate of 0.05.

Results

Participant Characteristics

In the CHAP trial,16 subjects attended 129 pharmacies during a 10 week period. Among the 15 889 individuals who participated in a CHAP session and had their AOBP measured, 13 449 (84.6%) provided consent and sufficient information to link their session results with Ontario administrative health data. A total of 6182 (46.0%) individuals were receiving antihypertensive medication, 2604 (19.4%) individuals were aged <66 years, 973 (7.2%) had missing self-reported risk factor information, and 63 (0.5%) had fewer than the minimum 3 years of Ontario Health Insurance Program coverage, leaving a final, evaluable study cohort of 3627 individuals.

The demographic and clinical characteristics of study subjects are presented in Table 1. Their mean (SD) age was 75.2 (5.8) years. Forty-one percent were males, 687 (18.9%) were aged ≥80 years, and 36.2% had a diagnosis of hypertension. Mean BP was 132.1 (18.7)/75.1 (10.5) mm Hg. There were few smokers (7.3%), but 31.0% self-reported having high cholesterol levels. The mean (SD) follow-up time was 4.9 (1.0) years.

Cardiovascular Outcomes in Relation to Blood Pressure

There were a total of 208 nonfatal cardiovascular events and 63 fatal cardiovascular events for a total of 271 composite outcomes. The crude event rates per 1000 person years for each 10 mm Hg category of systolic and diastolic BP and pulse pressure are shown in Table 2. Systolic BP showed a progressive increase in the crude event rate/1000 patient-years starting at 130 to 139 mm Hg and reaching a plateau at 150 mm Hg. The event rates for diastolic BP began increasing at 80 to 89 mm Hg. There were too few subjects with a diastolic BP of ≥100 mm Hg to examine the cardiovascular risks associated with readings above this level.

Adjusted hazard ratios with 95% confidence intervals according to category of pulse pressure.

Discussion

The CHAP trial presented the first opportunity to relate AOBP readings to the development of future cardiovascular events. In community-dwelling individuals who were >65 years, AOBP in the category of 135 to 144/80 to 89 mm Hg was associated with a significant increase in risk for nonfatal or fatal cardiovascular events over a mean follow-up of 4.9 years. A pulse pressure of >80 mm Hg was also associated with an elevated risk of future cardiovascular events. None of the participants was receiving antihypertensive drug therapy at baseline. All BP readings were taken in a community pharmacy in accordance with standard procedures for AOBP, making the results applicable to office practice.

Before assessing the implications of these findings to the clinical setting, it would be helpful to review how BP cut points for diagnosing hypertension have evolved. The cut point of 140/90 mm Hg for the mercury sphygmomanometer was first selected arbitrarily with no evidence for any distinct increase in cardiovascular events or death at this level of BP. Most of the early data on mortality related to BP status came from statistics collected by the insurance industry, which showed the association between BP and death to be continuous, with a gradient in risk down into the normal BP range.27 The cut point of 90 mm Hg was subsequently supported by the Veterans Affairs Study28 reported in 1970, which showed a reduction in cardiovascular events when a diastolic BP of 90 to 114 mm Hg was treated with medication. Two decades later, the Systolic Hypertension in the Elderly trial28 found clinical benefit in treating a systolic BP of ≥160 mm Hg. To date, there have not been any similar studies to support 140 mm Hg as the cut point for treating uncomplicated essential hypertension.

In the mid-1990s, 24-hour ABPM started to be used more widely in clinical practice. The first attempt at defining a normal ambulatory BP was made in 1996 by an American Society of Hypertension expert group led by Tom Pickering.29 A cut-point of 140/90 mm Hg for diagnosing hypertension according to ABPM was defined by examining studies which compared the mean awake ambulatory BP to the mean manual office. In 1999, the Canadian Hypertension Society proposed guidelines30 for using ABPM to diagnose hypertension based on the same comparative data used by Pickering et al supplemented by cardiovascular outcome data from a Japanese study31 on ABPM in a large community-based population. In this study, the lowest quintile for 24-hour ambulatory BP was arbitrarily set at an HR of 1.0, and the quintile with a significantly higher HR was designated as the cut point for hypertension. Using these data, the Canadian Hypertension Society confirmed 135/85 mm Hg for the diagnosis of hypertension using ABPM. To define a cut point for hypertension using AOBP, we used a similar approach to complement existing comparative AOBP/ABPM data with hard cardiovascular end-points

Numerous comparative studies9 involving both treated and untreated hypertensive patients have shown AOBP readings to be equivalent to the current gold standard for defining hypertension, the awake ambulatory BP, which has led to 135/85 mm Hg as the cut point for AOBP. The findings in the present study in an older population confirm a cut point of 135 mm Hg systolic for diagnosing hypertension because readings in a range of 135 to 144 mm Hg were associated with a significant increase in cardiovascular events. The cut point for diastolic BP (80 mm Hg) associated with a significant increase in risk was slightly lower than for ABPM.1 The 5 mm Hg difference may be attributed to the older age of the CHAP population, with an increase in arterial stiffness leading to a lower diastolic BP with a resulting higher pulse pressure. In recent reports, a lower diastolic pressure32 and a higher pulse pressure33 were independently predictive of an increase in cardiovascular events. The present findings are consistent with these observations in that there was a significant increase in cardiovascular events at a diastolic BP <80 mm Hg and at a pulse pressure ≥80 mm Hg.

In comparative studies,8 AOBP is ≈5/5 mm Hg lower than a manual BP or semiautomated electronic BP recorded using standard guidelines for proper office BP measurement. It should be noted that there was an increase in cardiovascular risk within the usual normal range for office BP in the present study, which is exactly what has been seen with manual BP starting at readings of 110 to 120/70 to 80 mm Hg.34 Given that cut points for defining hypertension are somewhat arbitrary, the results of the present study taken together with existing comparative data for AOBP versus awake ambulatory BP, manual office BP and home BP, support using a cut point of 135/85 mm Hg for defining hypertension in the general population, the same cut point as for ABPM and home BP.

The present study is timely in that recent international4 and Canadian18 guidelines now recommend AOBP as the preferred method for recording BP in the office setting. AOBP is recognized as being more accurate based on several studies, including a randomized controlled trial involving 555 hypertensive patients comparing AOBP use with conventional manual BP in the management of patients in routine clinical practice.35 AOBP eliminates the white coat effect and is less subject to digit preference (rounding off readings to the nearest zero) on the part of the observer.9 Devices currently available for AOBP are set to take multiple readings automatically, whereas single BP readings are common with manual BP.

The present study does have several limitations. The population was over age 65, with a mean age of 74 years. Thus, the present findings may not pertain to younger persons. Some cardiovascular risk factors included in the adjusted analysis, such as smoking and high blood cholesterol, were self-reported by the subjects. There were few individuals with stage 2 or stage 3 hypertension, and the sample was derived from a population known to have hypertension treatment and control rates of ≈65%.36 However, improvements in the management of hypertension in developed countries are making their populations more like the present cohort than before. Nonetheless, the findings in the CHAP population may not represent all areas of the world, especially where hypertension control rates are much lower and access to automated sphygmomanometers is limited.

AOBP is more accurate and more reliable than manual office BP in routine clinical practice and is not subject to the white coat effect. AOBP correlates with other intermediate measures of target organ damage, such as left ventricular mass, as strongly as does ABPM.15 Mean AOBP readings are comparable to mean awake ambulatory BP and to home BP. The present study which related AOBP to future cardiovascular end points, now presents further evidence to support an AOBP reading of ≥135/85 mm Hg for making a diagnose of hypertension.

Perspectives

This study is the first attempt to relate cardiovascular outcomes to AOBP measurement. The increase in cardiovascular events noted in this older community-dwelling population is consistent with using ≥135/85 as the cut point for diagnosing hypertension using AOBP. Until now, there has been some reluctance to adopt AOBP, even though there is strong evidence that AOBP readings are more accurate than manual BP and are not associated with the white coat effect frequently seen with manual BP in routine clinical practice. Although our findings are limited to persons >65 years, they are still relevant to the majority of the hypertensive population. AOBP is already recommended in Canadian and European guidelines, and its use should become more widespread now that there is an evidence-based rationale for implementing this technique into routine clinical practice.

Acknowledgments

We thank Brogan Inc, Ottawa, for use of their Drug Product and Therapeutic Class Database. The opinions, results, and conclusions reported in this article are those of the authors and are independent from the funding sources. No endorsement by Institute for Clinical Evaluative Sciences or the Ontario Ministry of Health and Long-Term Care is intended or should be inferred.

Sources of Funding

This study was supported by a grant from the Canadian Institutes of Health Research and by the Institute for Clinical Evaluative Sciences, a nonprofit research institute funded by the Ontario Ministry of Health and Long-Term Care. The study sponsors had no role in designing the study; collecting, analyzing, or interpreting the data; writing the report; or in the decision to submit the article for publication.

References

; European Society of Hypertension Working Group on Blood Pressure Monitoring. European Society of Hypertension position paper on ambulatory blood pressure monitoring.J Hypertens. 2013;31:1731–1768. doi: 10.1097/HJH.0b013e328363e964.

; ESH Working Group on Blood Pressure Monitoring. European Society of Hypertension guidelines for blood pressure monitoring at home: a summary report of the Second International Consensus Conference on Home Blood Pressure Monitoring.J Hypertens. 2008;26:1505–1526. doi: 10.1097/HJH.0b013e328308da66.

; Task Force Members. 2013 ESH/ESC Guidelines for the management of arterial hypertension: the Task Force for the management of arterial hypertension of the European Society of Hypertension (ESH) and of the European Society of Cardiology (ESC).J Hypertens. 2013;31:1281–1357. doi: 10.1097/01.hjh.0000431740.32696.cc.

. Clinical practice guidelines for the management of hypertension in the community a statement by the American Society of Hypertension and the International Society of Hypertension.J Hypertens. 2014;32:3–15. doi: 10.1097/HJH.0000000000000065.

Comparisons of automated blood pressures in a primary health care setting with self-measurements at the office and at home using the Omron i-C10 device.Blood Press Monit. 2015;20:98–103. doi: 10.1097/MBP.0000000000000088.

Novelty and Significance

What Is New?

The cardiovascular risk in relation to blood pressure recorded using a fully automated, electronic sphygmomanometer specifically designed for office use was determined in community-dwelling persons aged 66 years and older.

What Is Relevant?

There are now clinical outcome data to support using 135/85 mm Hg as a cut-point for diagnosing hypertension using automated office BP in routine clinical practice.

Summary

By following 3627 older persons who had their blood pressure recorded using a fully automated sphygmomanometer for the development of nonfatal and fatal cardiovascular events, we were able to determine the blood pressure level at which cardiovascular risk increases. For these untreated subjects, cardiovascular risk increased at 135 to 144/80 to 89 mm Hg, which supports using the cut-point derived previously from comparative BP measurement data of 135/85 mm Hg to diagnose hypertension using automated recorders. This cut-point is the same as for the awake ambulatory and home blood pressure.